The present invention relates generally to magnetic recording media, and more particularly to high density magnetic recording disks having improved recording characteristics.
Thin film magnetic recording disks generally comprise a disk substrate having a magnetic layer and a number of underlayers and overlayers deposited thereon. The nature and composition of each layer is selected to provide the desired magnetic recording characteristics, as generally recognized in the industry. An exemplary present day thin film disk is illustrated in FIG. 1 and comprises a non-magnetic disk substrate 10, typically composed of aluminum or an aluminum alloy. An amorphous nickel-phosphorus (NiP) layer 12 is formed over each surface of the disk substrate 10, typically by plating. The NiP layer is hard, and imparts rigidity to the aluminum substrate. A second underlayer in the form of a chromium ground layer 14 is formed over the NiP layer 12, typically by sputtering, and a magnetic layer 16 is formed over the ground layer 14. The magnetic layer 16 comprises a thin film of a ferromagnetic material, such as a magnetic oxide or magnetic alloy. Usually, a protective layer 18, such as carbon film, is formed over the magnetic layer 16, and a lubricating layer 20 is formed over the protective layer.
The presence of the NiP layer 12 and the chromium ground layer 14 have been found to improve the recording characteristics of the magnetic layer 16. In particular, a chromium ground layer formed over a NiP layer has been found to provide enhanced coercivity and reduced noise characteristics. Additionally, the NiP layer is often mechanically textured to create a roughened surface prior to formation of the chromium ground layer. This surface texturing has a substantial effect on the mechanical properties of the disk and its interaction with the recording transducer (read/write head), which typically xe2x80x9cfliesxe2x80x9d over the disk surface on a cushion of air that is moved by the rotating disk. In particular, texturizing is highly beneficial to the magnetic recording system""s ability to reliably withstand repeated starting and stopping of the disk, with its associated repeated contact between the read/write head and the disk""s surface. The texturing may be circumferential, crosswise, or separated into start/stop and data zones, with the preferred geometry depending on the particular composition of the cobalt-containing magnetic layer, and on the specific disk drive design.
Such magnetic recording constructions have been very successful and allow for relatively high recording densities. As with all successes, however, it is desired to provide magnetic recording disks having even higher recording densities. To increase recording densities beyond those of known practical magnetic recording media, it would be beneficial to promote certain types of crystal growth in the magnetic recording layer within the structure of the magnetic recording media.
For this reason, it is desirable to have improved recording media having underlayers made of specific materials that promote improved performance in the magnetic layer of the recording media. It would be particularly desirable if such improved magnetic recording media were readily fabricated using existing thin film deposition and texturing equipment. It is also desirable if the underlayer further enhances the magnetic properties of recent cobalt-containing magnetic layers.
The present invention is directed to improved magnetic recording media. The underlayer used in the structure of magnetic recording media can effect the epitaxial crystal growth in the overlying magnetic recording layer, and the underlayer can be chosen to increase certain desired characteristics in the bulk magnetics and parametrics of the recording media. Specifically, certain materials in the underlayer promote a smaller grain size and a more equally spaced crystal distribution in the magnetic layer which generally increases the performance of the magnetic layer.
The present invention provides magnetic recording media comprising a rigid substrate and an underlayer disposed over the substrate, in which the underlayer comprises a chromium molybdenum (CrMo) alloy. A magnetic layer is disposed over this underlayer, and is also disposed over a texturized surface. Generally, the substrate comprises aluminum, and an NiP layer is disposed over the substrate and below the underlayer. Preferably, the crystals in the CrMo underlayer are oriented with the (002) crystal plane parallel to the surface of the substrate. Additionally, the (002) crystal size in a film growth direction is at least about 140 xc3x85. The large crystal size is believed to facilitate epitaxial growth of the overlying magnetic layer. Advantageously, recording media with such a (002) crystal orientation, when used with a magnetic layer such as CoCrTaPtNi, exhibit significantly higher parametric qualities than underlayers using other materials. These improved parametric qualities will allow the recording media to have higher recording densities.
Typically, Mo in the range between about 7% and 16% (atomic percent) in the CrMo alloy, more preferably between about 9% and 11%, will provide the recited (002) crystal orientation and preferred lattice constant for a better epitaxial growth with Co-alloy. Most preferably, underlayers will have about 10% Mo by atomic percent (Cr10Mo). It is believed that CrMo underlayer defines a surface that promotes evenly distributed epitaxial growth of Co crystals in the magnetic layer. The surface may also minimize the lateral crystal grain size of Co crystals in the magnetic layer. Preferably, the magnetic layer has Co crystals between about 60-150 xc3x85 in lateral crystal size. These characteristics of the magnetic layer improve the performance characteristics of the resulting recording media.
A further understanding of the nature and advantages of the invention may be realized by reference to the remaining portions of the specification and the drawings.